An aliphatic polycarbonate is a biodegradable copolymer, is a material useful for packages or coatings. The method for preparing a polycarbonate from epoxides and CO2 is highly environmental-friendly considering that any harmful compound phosgene is not used and that CO2 is taken with low cost.
Since 1960s, various types of catalysts have been developed to prepare polycarbonate from epoxides and CO2. Recently, the present inventor has disclosed highly-active and highly-selective catalyst synthesized from Salen [Salen: ([H2Salen-N,N′-bis(3,5-dialkylsalicylidene)-1,2-ethylenediamine]-type ligand including the quaternary ammonium salt [Bun-Yeoul Lee, Korean Patent No. 10-083358 (Registration date: Aug. 13, 2000); Bun-Yeoul Lee, Sujith S, Eun-Kyung Noh, Jae-Ki Min, Korean Patent Application No. 10-2008-0015454 (Filing date: Feb. 10, 2008); Bun-Yeoul Lee, Sujith S, Eun-Kyung Noh, Jae-Ki Min, PCT/KR2008/002453 (Filing date: Apr. 30, 2008); Eun Kyung Noh, Sung Jae Na, Sujith S, Sang-Wook Kim, and Bun Yeoul Lee*, J. Am Chem. Soc. 2007, 129, 8082-8083 (2007, Jul. 4); Sujith S, Jae Ki Min, Jong Eon Seong, Sung Jea Na, and Bun Yeoul Lee, Angew. Chem. Int. Ed., 2008, 47, 7306-7309. (2008, Sep. 8)]. The catalyst disclosed by the present inventor shows high-activity and high-selectivity, can be used for preparing high molecular weight copolymer, and is commercially applicable due to the polymerization at high temperature. Furthermore, since the ligand includes the quaternary ammonium salt, it has an advantage of easy recovery and recycling the catalyst after polymerization.
Furthermore, the present inventor has carefully analyzed the structure of the catalyst showing especially high-activity and high-selectivity among a group of catalysts of said patent, and therefore proved that the structure is unique, unknown before in which a nitrogen atom of Salen-ligand is not coordinated but oxygen atoms are coordinated to a metal atom (example 1). Accordingly, the invention relating to a new type of catalyst system obtained from the result filed as Korean Patent Application No. 10-2008-0074435 (Filing: 2008, Jul. 30).